A pair of white-tailed eagles – sea eagles - have successfully hatched two chicks in their tree-top nest - blissfully unaware of the threat that has hung over them since the eggs were laid.

A short distance from Tromsø in the north of Norway, a pair of white-tailed eagles has built an eyrie. They are almost urban birds. Despite icy winds and occasional snow showers, as winter gave way to spring the female laid two eggs. Now the two are busy raising their rapidly growing chicks.

No matter what the weather, the parent birds remain at their self-imposed task, taking it in turns to sit on the eggs and protect them from the elements. When the eggs hatch, and while the youngsters are being fed and cared for by their untiring parents, from their lofty perch they have an unimpaired view of the Arctic Ocean.

Outwardly, the situation is idyllic, but in reality the little family is threatened by an insidious, unseen enemy. Recent generations of Norway’s white-tailed eagles have been forced to live with environmental toxins in their systems – and new poisons are constantly appearing. These man-made air- and water-borne toxins poison the fish on which the eagles feed. The Norwegian Institute for Nature Research (NINA) keeps a close watch on the country’s eagle population, and in this programme we accompany the Institute’s Trond Johnsen when he takes the chicks down from their nest and subjects them to a thorough health check.